This application focuses on new therapies for cognitive impairment in multiple sclerosis, in response to PAR- 14-088, a new Direct-to-Phase II SBIR grant mechanism to enhance the pace of technological development and commercialization. We have demonstrated the ability of MLK inhibition (MLKi) to efficaciously protect hippocampal synaptic architecture and reduce microglial activation in an experimental autoimmune encephalomyelitis (EAE) model of cognitive impairment in MS. We have synthesized and characterized, two drug-like molecules with different structures, one of which we will advance as a potential clinical compound for the treatment of cognitive impairment in MS based on its profile of efficacy in our in vivo models. We will also obtain IND supporting safety study data to allow partnering of the compound for clinical development. The need for new therapies for cognitive impairment in MS is urgent, because current therapies, while effective at preventing relapses, do not prevent progressive cognitive deficits that can profoundly impact independence, quality of life and activities of daily living. Neuroimaging studies suggest that these symptoms derive largely from widespread degeneration of gray matter in the brain and progress independently of the relapses and focal white matter inflammation that are the targets of current immunosuppressive drugs. Activation of microglia in MS gray matter, which can occur widely even without ongoing relapses, has been associated with loss of synaptic connections and increases in markers of neuronal injury. Activated microglia release the excitatory neurotransmitter glutamate, in addition to radicals and pro-inflammatory molecules that can augment glutamate's neurotoxic effects. Increased concentrations of these molecules in studies of MS patients suggest a substrate for excitotoxic injury in MS gray matter. In an in vivo EAE model of MS, we have demonstrated that twice daily (10 mg/kg, ip) dosing of the MLK3 inhibitor URMC-099, at the onset of motor symptoms, efficaciously protects hippocampal synaptic architecture and reduces microglial activation, without affecting motor deficits that arise from spinal cord damage. URMC-099, with excellent CNS penetration and apparent safety, while a very potent inhibitor of MLK3 is not a selective MLK inhibitor. CLFB-1134, also a drug like molecule with excellent CNS penetration is a highly selective inhibitor of MLK3. We will identify which agent is more efficacious preventing microglia-associated synaptic degeneration in our in vivo murine EAE model. Quantitative anatomic assessment of synaptic elements will be used to answer whether selective vs. non- selective MLK3 inhibition provides superior efficacy. Quantitative electrophysiologic parameters will be ascertained to determine whether URMC-099 vs. CLFB-1134 treatment provides greater functional restoration of hippocampal synapses. The most efficacious compound will be advanced for a preclinical data package to support IND filing. With over 2.3 million people worldwide living with MS, and up to 70% having some type of cognitive impairment, as many as 1.6 million people may benefit from this therapeutic approach.